The path to building a $1 million investment portfolio isn't rocket science, and it doesn't involve buying risky rocket stocks like Space Exploration Technologies. Instead, it's a simple combination of picking the right exchange-traded fund (ETF), contributing to it regularly, and patiently letting the S&P 500 grow over time.

And one of the best ways to do this is by owning the Vanguard S&P ETF (NYSEMKT: VOO).

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Here's why owning this Vanguard ETF could help you reach your $1 million portfolio goal.

You don't have to be an expert stock picker

As its name suggests, the Vanguard S&P 500 ETF tracks the S&P 500 index. This means that your investments will be spread across nearly 500 leading publicly traded companies.

If artificial intelligence (AI) stocks are doing well -- and they've done very well lately -- your portfolio will benefit because many of the largest companies in the S&P 500 are tech companies. Still, if the energy sector is performing well, or consumer goods stocks climb higher, you won't miss out on those returns either because the Vanguard S&P 500 ETF is spread across all market sectors.

There's a two-fold benefit here. The first is that you don't have to be an expert stock picker to benefit. You don't have to hunt for the latest investment trends or pick the best companies; you just have to own the ETF.

And secondly, your portfolio is instantly diversified from the start. This is incredibly helpful if you're unsure about a market sector or don't want to spend time learning about companies far outside your interests.

How the Vanguard S&P 500 ETF can help you achieve a $1 million portfolio

To reach $1 million in your portfolio, you'll have to do something that many investors find very difficult: be patient.

Since 1957, the S&P 500 has had a historic average annual return of about 10%. Some years, the market does far better than 10% returns, and some years it trades in the red. And there are many months, even during good years, where stocks are very volatile.

This volatility causes many people to pull their money out of the market and wait for brighter days.

Instead, the trick to achieving $1 million is to consistently invest your money (no matter what's happening with the market) and stay invested for decades. Here are some examples: